Copying documents by a camera goes back to the beginnings of photography. It is done in duplicating or restoring damaged photographs, to change size or emphasis in a picture, to produce a microphotograph of printed or pictorial material (microfile) or to prepare printing plates or other material for printing books, magazines, newspapers etc.
Very special and very sophisticated cameras are used for copying documents. Some such cameras are built into the structure of the laboratories where they are used, so that the film is fed into and out of the camera and is developed in the darkroom which, in effect, is part of the camera equipment.
The art of focusing copying cameras is well represented in Class 355, sub classes 44, 55, 61, 62 and 63. Some patents of interest that may be mentioned are as follows:
U.S. Pat. No. 2,082,170 to McRae shows a device for focusing an enlarger. The real image projected onto the easel is reflected by a mirror so that it falls on the underside of a ground glass. The image is then observed from above the ground glass. This is usually easier to do than looking directly at the easel.
A similar device is shown in U.S. Pat. No. 2,100,324 to Castle except that here the image on the ground glass is viewed thru a magnifying glass.
U.S. Pat. No. 2,791,936 carries the above ideas one step further. Here, instead of placing the real image on a ground glass, the image is directed into a magnifier. The magnifier is focused on the plane that contains the image. Thus the image is seen "in air" and the "noise" of the ground glass is avoided.
The art of copying images or projecting images onto paper, photographic emulsions, or solid state wafer surfaces is very extensive but we found no art where a bright virtual image is projected into the plane of the surface of interest. Mirrors are used to manipulate or move the image for repeat exposures (U.S. Pat. No. 4,425,037); to produce multiple images (U.S. Pat. No. 4,788,576); or to project special registration lines onto a suitable easel (U.S. Pat. No. 4,244,649). Our invention is not intented to replace the automatic means built into the elaborate cameras of the extensive art of large copying cameras. It is a relatively simple device to help the operator of a camera to optimize the setting of his or her camera to obtain the sharpest image of the document or a surface being photographed.